CfllTIN IN THE CARTILAGES OF LIMULUS AND SEPIA. 
179 
Its action upon polarized light. 
Its ready solubility in water. 
Its slight solubility in alcohol. 
Comparing the properties of the crystals under these four 
heads, we find them to be similar in every respect ; the irre- 
sistible conclusion is, therefore, that the crystalline substance 
obtained from the cartilage of Sepia is hydrochlorate of glyco- 
samine, and that the cartilage of Sepia contains chitin. 
The question now remains, how much chitin does this car- 
tilage contain ? the method I have adopted in the quantitative 
analysis has been the following : 
A known weight of cartilage is taken, and potash added to 
it ; the residue is washed, collected on a dried and weighed 
filter ; it is then dried at 100° C., and weighed ; the increase in 
weight gives the weight of the precipitate in the dry form, 
from this the amount of ash is deducted, and from the 
remainder the percentage can be calculated. 
The average of two such quantitative experiments gives the 
percentage of chitin in the cartilage of Sepia as T22. 
B. — Composition of the Entosternite of Limulus. 
What has been said for the cartilage of Sepia may be 
repeated in very good measure for the cartilaginous Entoster- 
nite of the king-crab. The method of analysis was the same, 
and the results are as follows : 
The greater part of the ground substance is composed of a 
chondrin-like body, giving the tests for mucin, and to some 
extent also those for gelatin (viz. precipitation by tannin, lead 
acetate, mercuric chloride, ferrocyanide of potassium, and acetic 
acid) ; but not sufficient gelatin is present to cause gelatiniza- 
tion to occur in cooling the hot watery solution. 
Keratin and elastin are absent. 
Chitin is present : this is shown by — 
1. There is a residue insoluble in boiling alkalies, soluble in 
cold concentrated hydrochloric acid ; the addition of water 
reprecipitating it from its solution. 
